US4490725A - Log-periodic antenna - Google Patents
Log-periodic antenna Download PDFInfo
- Publication number
- US4490725A US4490725A US06/537,777 US53777783A US4490725A US 4490725 A US4490725 A US 4490725A US 53777783 A US53777783 A US 53777783A US 4490725 A US4490725 A US 4490725A
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- 239000004020 conductor Substances 0.000 claims abstract description 38
- 238000003491 array Methods 0.000 claims abstract description 25
- 230000007423 decrease Effects 0.000 claims description 5
- 230000001154 acute effect Effects 0.000 claims 2
- 230000010287 polarization Effects 0.000 claims 1
- 230000000737 periodic effect Effects 0.000 abstract description 11
- 238000013459 approach Methods 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 4
- 239000011358 absorbing material Substances 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- 239000004593 Epoxy Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 239000003989 dielectric material Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000011152 fibreglass Substances 0.000 description 1
- 238000000034 method Methods 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q11/00—Electrically-long antennas having dimensions more than twice the shortest operating wavelength and consisting of conductive active radiating elements
- H01Q11/02—Non-resonant antennas, e.g. travelling-wave antenna
- H01Q11/10—Logperiodic antennas
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q25/00—Antennas or antenna systems providing at least two radiating patterns
- H01Q25/02—Antennas or antenna systems providing at least two radiating patterns providing sum and difference patterns
Definitions
- This invention relates to frequency independent antennas and more particularly to frequency independent log-periodic antenna arrays.
- Log-periodic antennas are arrayed together to provide higher directivity and higher gain and also to adapt the antennas for use in direction finding and tracking applications.
- Such uses of arrayed log-periodic antennas provide independent error curves for either amplitude comparison of for sum and difference derivations.
- a problem with such arrays is the periodic occurrence of gain variations in the E-plane (horizontal) arrays of the antenna across the operating band. These periodic gain variations or "dropouts" are accompanied by pattern deteriorations and seriously adversely affect the performance of the antenna.
- This invention is directed to a frequency independent antenna that overcomes this gain dropout anomaly.
- a general object of the invention is the provision of a log-periodic antenna having arrays of elements in the E-plane operating over the frequency band of the antenna without gain dropouts.
- a further object is the provision of such an antenna in which periodic gain dropouts are eliminated without otherwise detracting from the performance characteristics of the antenna.
- a shielded balanced feed line for energizing log-periodic antenna elements arrayed in a frequency independent manner in the E-plane.
- a preferred form of the shielded feed line is the inner conductor of a coaxial cable.
- FIG. 1 is a schematic plan view of a log-periodic dipole antenna embodying this invention.
- FIG. 2 is a perspective view of one of the arrays of FIG. 1 with parts of the feed lines broken away to show details of construction.
- FIG. 3 is a schematic plan view similar to FIG. 1 showing arrays having a zig-zag pattern of radiating elements.
- FIG. 4 is an enlarged perspective view of one of the arrays of FIG. 3.
- FIG. 5 is a greatly enlarged portion of FIG. 4 showing the connection of the feed lines to the radiating elements.
- FIG. 6 is a greatly enlarged plan view of a portion of the zig-zag shaped conductive strip of FIGS. 3-5 showing design parameters.
- FIG. 7 is a perspective view of an array of a log-periodic antenna designed for circularly polarized operation and embodying the invention.
- FIG. 8 is an enlarged end view of the array taken on line 8--8 of FIG. 7.
- FIG. 9 is a schematic representation of two of the arrays of FIG. 7 disposed to provide direction finding information.
- FIG. 1 illustrates an antenna 10 embodying the invention and comprising dipole arrays 11 and 12 in a horizontal (E) plane, the axes 13 and 14 of arrays 11 and 12, respectively, forming an angle ⁇ .
- Arrays 11 and 12 have feed lines 16 and 17, respectively, connected to hybrid T junctions 18 and 19, respectively, also known as magic T junctions.
- the outputs of the magic T junctions 18 and 19 are connected to a power divider 21 which in turn is connected to utility apparatus such as a receiver or transmitter.
- Antenna arrays 11 and 12 are substantially identical in construction and accordingly only one of them, array 11, is shown in FIG. 2 and is described.
- Feed line 16 of array 11 comprises vertically stacked coaxial cables 23 and 24 having inner conductors 25 and 26, respectively, and outer conductors 27 and 28, respectively. The outer conductors are grounded as indicated at 29 and thus shield the inner conductors. Cables 23 and 24 are connected to magic T 18 which provides 180° phase reversal in the two lines as required for end fire radiation along array axis 13.
- Radiating elements 30 are connected to the feed lines transversely of the array axis 13 such that element dimensions and interelement spacings decrease from a maximum at one end to a minimum at the other in increments of a predetermined ratio ⁇ .
- These elements comprise a first set a, b, c, d and e connected to inner conductor 25 of cable 23 and a second set a', b', c', d' and e' connected to inner conductor 26 of cable 24.
- Each element extends through an opening in the outer conductor of the associated cable for direct electrical contact with the inner conductor thereof.
- each array is arranged in transversely extending pairs, each pair being designated by the same letter a-a', b-b', etc.) and each pair comprising one dipole.
- Inner conductors 25 and 26 are the balanced feed lines for the array and by connecting them to the radiating elements and by grounding outer conductors 27 and 28 as described, the feed lines are shielded from external radiation including the effects of mutual coupling between arrays 11 and 12. By use of these shielded feed lines, periodic gain variations across the operating band of the antenna are eliminated.
- a log-periodic dipole antenna 10 constructed as described above had the following design parameters and performance characteristics:
- the feeder impedance is 100 ohms because 50 ohm coaxial cables were used.
- This antenna provides pseudo-frequency independent performance similar to a log-periodic dipole antenna fed by conventional balanced lines. When two dipole arrays are arrayed in the frequency independent manner at relatively close spacing, i.e., 0.5 wavelength the antenna provided substantially frequency independent performance with no periodic gain dropouts or pattern deteriorations.
- the dipole antenna described above is constructed to operate at UHF frequencies readily but not at microwave frequencies due to the physical size of the balun and the manner in which the radiators are attached to the transmission lines.
- Periodic gain dropouts and pattern deteriorations are not limited to E-plane arrays of the planar log-periodic dipole antennas of the type described above.
- Open structure types of log-periodic antennas comprising E-plane arrays with the radiating elements of each array in two planes converging to the feed point also have periodic gain dropouts when arrayed in the frequency independent manner.
- An example of such open type structure is illustrated in FIGS. 3 and 4 and comprises antenna 35 having substantially identical arrays 36 and 37, each array having two sets of radiating elements converging at an angle ⁇ in the H-plane (vertical).
- the angle ⁇ determines the H-plane beamwidth and the mean level of the input impedance of the antenna and distinguishes the "open" structure from the planar antenna. In other words, when the angle ⁇ approaches 0, a planar antenna comparable to the above described log-periodic dipole antenna results.
- Arrays 36 and 37 have axes 38 and 39 respectively, which converge at an angle ⁇ toward the feed points of the arrays, and in accordance with this invention, are fed by balanced lines 41 and 42, respectively. These arrays are substantially identical and accordingly only one of them, array 36, is described.
- Feed line 41 comprises the inner conductors 43a and 44a of coaxial cables 43 and 44, respectively, see FIGS. 4 and 5. Cables of lines 41 and 42 are connected to magic T couplers 45 and 46, respectively, which in turn are connected to a power divider 47 for connection to associated utility apparatus.
- Array 36 comprises a pair of conductive strips 50 and 51 in tapered zig-zag shapes forming triangularly shaped radiating elements.
- Strips 50 and 51 are mounted on elongated support members 52 and 53, respectively, composed of dielectric material such as epoxy fiberglass.
- the outer conductors of coaxial cables 43 and 44 are suitably grounded and the inner conductors 43a and 44a thereof are connected to strips 50 and 51, respectively, at the converging end of the array to constitute the feed point.
- segments 50 and 51 having the same spacing from the array feed point project equal distances and in opposite directions from supports 52 and 53, respectively, and constitute the radiating elements of the array.
- segment 50a of strip 50 and segment 51a of strip 51 are equally spaced from the feed point and project equal distances and in opposite directions from supports 52 and 53, respectively.
- Segments 50a and 51a thus have equal lengths and constitute one radiating element of the array analogous to a dipole of array 11.
- the continuous zig-zag shaped conductive strip is defined by two conventional log-periodic design parameters ⁇ see FIG. 6, and ⁇ .
- An additional design parameter ⁇ defines the width of the zig-zag conductor.
- the antenna structure approaches that of a zig-zag wire.
- the width of the zig-zag conductor increases until ⁇ approaches 0.
- the array structure consisting of two of these zig-zag conductors performs similarly to the conventional log-periodic dipole array with the exception of a slight loss of gain due to the I 2 R loss.
- the exciting currents instead of travelling straight on the metallic boom of the conventional antenna, follow the zig-zag conductor path before reaching the active region of the array.
- the loss is less than 1 dB. By decreasing the angle ⁇ this loss is minimized with the tradeoff of a slight increase in the amount of conductive material.
- the spacings l 0 , l 1 , l 2 , . . . l n of the elements from the point of convergence as illustrated in FIG. 6 are related to each other log-periodically in accordance with the following formulae:
- a circularly polarized antenna embodying the invention was constructed by substituting a 90° coupler for the power divider 47 in FIG. 3 and such antenna had the following parameters:
- FIGS. 7, 8 and 9 depicting a circularly polarized antenna array 55 comprising four zig-zag conductive strips 56, 57, 58 and 59, similar to the strips shown in FIG. 6 and mounted on the plane sides of a pyramid-like dielectric support 60. Adjacent sides of support 60 are at right angles to each other and taper from a maximum dimension at one end to a minimum dimension at the other. Each of the strips is similarly tapered to the feed point of each at the end having the minimum dimension. The planes of adjacent strips are likewise perpendicular to each other as shown in FIGS. 7 and 8.
- the array 55 is fed by the inner conductors 62, 63 and 64 and 65 of coaxial cables, the other conductors of which are connected to ground. Cables having conductors 62 and 64 are connected to magic T 67 and cables having conductors 63 and 65 are connected to magic T 68. Each magic T is connected to a 90° coupler 69 which in turn is connected to associated utility apparatus. The magic T junctions 67 and 68 and the 90° coupler 69 are enclosed in a broken line block 70 for convenience of explanation of FIG. 9. When two such circularly polarized arrays 55 and 55' are arrayed together as shown in FIG. 9, the outputs of block 70 and identical block 70' may be combined in magic T 71 to provide direction finding data.
- the antenna is subject to the gain dropout anomaly when energized by conventional unshielded feed lines.
- the use of shielded feed lines for each of the array structures shown in FIG. 9 eliminates this gain dropout anomaly.
- FIGS. 7, 8 and 9 An antenna shown in FIGS. 7, 8 and 9 was constructed and operated from 0.25 to 4.0 GHz. The smallest and largest radiating elements were 0.8 inches and 26 inches, respectively. This frequency independent array was used as a direction finding antenna and operated over the above band without any periodic gain dropout anomaly.
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- Variable-Direction Aerials And Aerial Arrays (AREA)
Abstract
Description
______________________________________Convergence angle ε 26 Taper angle α 20° τ 0.9Smallest dipole 5"Largest dipole 16" Feed line impedance (Z.sub.0) 100 ohms Frequency band 470-900 MHz ______________________________________
______________________________________ l.sub.3 = √τ l.sub.4 l.sub.2 = √τ l.sub.3 l.sub.n-1 = √τ l.sub.η ______________________________________
______________________________________ α 20° β 7° √τ 0.9 Length of smallest element 0.3" Length of largest element 7.0" Frequency band 1 to 12 GHz ______________________________________
Claims (16)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US06/537,777 US4490725A (en) | 1981-10-09 | 1983-09-29 | Log-periodic antenna |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US30987481A | 1981-10-09 | 1981-10-09 | |
US06/537,777 US4490725A (en) | 1981-10-09 | 1983-09-29 | Log-periodic antenna |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US30987481A Continuation | 1981-10-09 | 1981-10-09 |
Publications (1)
Publication Number | Publication Date |
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US4490725A true US4490725A (en) | 1984-12-25 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US06/537,777 Expired - Lifetime US4490725A (en) | 1981-10-09 | 1983-09-29 | Log-periodic antenna |
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US (1) | US4490725A (en) |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4658262A (en) * | 1985-02-19 | 1987-04-14 | Duhamel Raymond H | Dual polarized sinuous antennas |
EP0434866A1 (en) * | 1988-12-14 | 1991-07-03 | Hughes Aircraft Company | Dual mode log periodic dipole antenna |
EP0709914A1 (en) * | 1994-10-25 | 1996-05-01 | Siemens Aktiengesellschaft | RF seeker head antenna system for missiles |
US20040075615A1 (en) * | 2001-06-19 | 2004-04-22 | Gregory Engargiola | Log-periodic anthenna |
US20040201541A1 (en) * | 2001-09-07 | 2004-10-14 | Izzat Narian K. | Wide bandwidth base station antenna and antenna array |
US20170237174A1 (en) * | 2016-02-12 | 2017-08-17 | Netgear, Inc. | Broad Band Diversity Antenna System |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3013268A (en) * | 1959-04-23 | 1961-12-12 | Collins Radio Co | Elliptical-polarized logarithmically periodic antenna |
US3366964A (en) * | 1964-10-20 | 1968-01-30 | Air Force Usa | Groundplane mounted log periodic antenna |
US3641579A (en) * | 1969-03-17 | 1972-02-08 | Textron Inc | FREQUENCY-INDEPENDENT IcR ANTENNA |
US3732572A (en) * | 1971-11-22 | 1973-05-08 | Gte Sylvania Inc | Log periodic antenna with foreshortened dipoles |
-
1983
- 1983-09-29 US US06/537,777 patent/US4490725A/en not_active Expired - Lifetime
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3013268A (en) * | 1959-04-23 | 1961-12-12 | Collins Radio Co | Elliptical-polarized logarithmically periodic antenna |
US3366964A (en) * | 1964-10-20 | 1968-01-30 | Air Force Usa | Groundplane mounted log periodic antenna |
US3641579A (en) * | 1969-03-17 | 1972-02-08 | Textron Inc | FREQUENCY-INDEPENDENT IcR ANTENNA |
US3732572A (en) * | 1971-11-22 | 1973-05-08 | Gte Sylvania Inc | Log periodic antenna with foreshortened dipoles |
Cited By (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4658262A (en) * | 1985-02-19 | 1987-04-14 | Duhamel Raymond H | Dual polarized sinuous antennas |
EP0434866A1 (en) * | 1988-12-14 | 1991-07-03 | Hughes Aircraft Company | Dual mode log periodic dipole antenna |
EP0709914A1 (en) * | 1994-10-25 | 1996-05-01 | Siemens Aktiengesellschaft | RF seeker head antenna system for missiles |
US5686929A (en) * | 1994-10-25 | 1997-11-11 | Siemens Aktiengesellschaft | RF homing head antenna system for missiles |
US20040075615A1 (en) * | 2001-06-19 | 2004-04-22 | Gregory Engargiola | Log-periodic anthenna |
US6952189B2 (en) | 2001-06-19 | 2005-10-04 | The Regents Of The University Of California | Log-periodic antenna |
US20040201541A1 (en) * | 2001-09-07 | 2004-10-14 | Izzat Narian K. | Wide bandwidth base station antenna and antenna array |
US6917346B2 (en) | 2001-09-07 | 2005-07-12 | Andrew Corporation | Wide bandwidth base station antenna and antenna array |
US20170237174A1 (en) * | 2016-02-12 | 2017-08-17 | Netgear, Inc. | Broad Band Diversity Antenna System |
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